1. Splash Screen

2. Five-Minute Check (over Lesson 7–6) CCSS Then/Now New Vocabulary
Example 1: Use a Scale Drawing
Example 2: Find the Scale
Example 3: Real-World Example: Construct a Scale Model
Lesson Menu

3. Determine whether the dilation from Figure A to Figure B is an enlargement or a reduction. Then find the scale factor of the dilation.
A. enlargement;
B. enlargement;
C. reduction;
D. reduction; __ 7 4
5-Minute Check 1

4. Determine whether the dilation from Figure A to Figure B is an enlargement or a reduction. Then find the scale factor of the dilation.
A. enlargement;
B. enlargement;
C. reduction;
D. reduction; __ 3 2
5-Minute Check 2

5. The coordinates of the vertices of two triangles are listed in the table. What is the scale factor of the dilation from ΔABC to ΔXYZ? A. B.
C. 2
D. 3 __ 7 4 1 2
5-Minute Check 3

6. Mathematical Practices 4 Model with mathematics.
Content Standards
G.MG.3 Apply geometric methods to solve problems (e.g., designing an object or structure to satisfy physical constraints or minimize cost; working with typographic grid systems based on ratios).
Mathematical Practices
4 Model with mathematics.
7 Look for and make use of structure.
CCSS

7. You used scale factors to solve problems with similar polygons.
Interpret scale models.
Use scale factors to solve problems.
Then/Now

8. scale model
scale drawing
scale
Vocabulary

9. Method 1 Write and solve a proportion.
Use a Scale Drawing
MAPS The distance between Boston and Chicago on a map is 9 inches. If the scale of the map is 1 inch: 95 miles, what is the actual distance from Boston to Chicago?
Method 1 Write and solve a proportion.
Let x represent the distance between Boston and Chicago.
Example 1

10. 1 ● x = 95 ● 9 Cross Products Property x = 855 miles Simplify.
Use a Scale Drawing
1 ● x = 95 ● 9 Cross Products Property
x = 855 miles Simplify.
Method 2 Write and solve an equation.
Let a = actual distance in miles between Boston and Chicago and m = map distance in inches. Write the scale as , which is 95 miles per inch. So for every inch on the map, the actual distance is 95 miles.
Example 1

11. Answer: The distance between Boston and Chicago is 855 miles.
Use a Scale Drawing
a = 95 ● m Write an equation.
= 95 ● 9 m = 9
= 855 Solve.
Answer: The distance between Boston and Chicago is 855 miles.
Check Use dimensional analysis. 
Example 1

12. MAPS The distance between Cheyenne, WY, and Tulsa, OK, on a map is 8 inches. If the scale of the map is 1 inch : 90 miles, what is the actual distance from Cheyenne to Tulsa?
A. 800 miles
B. 900 miles
C. 630 miles
D. 720 miles
Example 1

13. Answer: The scale of the model is 1 in. : 3.2 yd.
Find the Scale
A. SCALE MODEL A miniature replica of a fighter jet is 4 inches long. The actual length of the jet is yards. What is the scale of the model?
To find the scale, write the ratio of a replica length to an actual length.
Answer: The scale of the model is 1 in. : 3.2 yd.
Example 2

14. Find the Scale
B. SCALE MODEL A miniature replica of a fighter jet is 4 inches long. The actual length of the jet is yards. How many times as long as the actual is the model jet?
To answer this question, find the scale factor of the model. Multiply by a conversion factor that relates inches to yards to obtain a unitless ratio.
Answer: The scale factor is : 1. That is, the actual jet is times as long as the model.
Example 2

15. A. SCALE MODEL A miniature replica of a fire engine is 9 inches long
A. SCALE MODEL A miniature replica of a fire engine is 9 inches long. The actual length of the fire engine is 13.5 yards. What is the scale of the replica?
A. 2 in. : 3 yd
B. 1 in. : 3 yd
C. 2 in. : 5 yd
D. 3 in. : 4 yd
Example 2

16. B. SCALE MODEL A miniature replica of a fire engine is 9 inches long
B. SCALE MODEL A miniature replica of a fire engine is 9 inches long. The actual length of the fire engine is 13.5 yards. How many times as long as the model is the actual fire engine?
A. 48
B. 54
C. 60
D. 63
Example 2

17. The actual classroom is 20 feet wide.
Construct a Scale Model
SCALE DRAWING Gerrard is making a scale model of his classroom on an 11-by-17 inch sheet of paper. If the classroom is 20 feet by 32 feet, choose an appropriate scale for the drawing and determine the drawing’s dimensions.
The actual classroom is 20 feet wide.
20 feet ÷ 11 inches = 1.8 feet per inch
The actual classroom is 32 feet long.
32 feet ÷ 17 inches = 1.8 feet per inch
Example 3

18. Construct a Scale Model
A scale of 1 inch = 2 feet would be appropriate. So, for every inch on the paper p, let the actual measure a be 2 feet. Write this as an equation.
width:
a = 2 ● p Write an equation.
20 = 2 ● p a = 20
10 = p Divide each side by 2.
Example 3

19. Answer: 1 in. : 2 ft; 10 in. wide, 16 in. long
Construct a Scale Model
length:
a = 2 ● p Write an equation.
32 = 2 ● p a = 32
16 = p Divide each side by 2.
Answer: 1 in. : 2 ft; 10 in. wide, 16 in. long
Example 3

20. ARCHITECTURE Alaina is an architect making a scale model of a house in a 15-by-26 inch display. If the house is 84 feet by 144 feet, what would be the dimensions of the model using a scale of 1 in. : 6 ft?
A. 14 in. × 24 in.
B. 14 in. × 25 in.
C. 15 in. × 25 in.
D. 15 in. × 26 in.
Example 3

21. End of the Lesson